1. Technical Field
The present invention relates to, for example, a MEMS (Micro Electro Mechanical Systems) device in which a functional element, such as a resonator, a sensor and an actuator, and/or an electronic circuit are integrated on one substrate.
2. Related Art
For example, in a MEMS device that includes a resonator with capacitance as a functional element, the resonator is airtightly sealed, in a vacuum state, in a cavity formed in a substrate. Also, even in the case of a functional element that does not require airtight vacuum seal, the functional element is airtightly sealed in a cavity so as to prevent the influences of dust, moisture, and the like.
In order to form a cavity in such a MEMS device, for example, a sacrificial film is formed in a cavity provided with a functional element, the cavity is covered by a first lid portion in which an opening (release hole) is formed in a predetermined position, and then the sacrificial film is removed through release etching. Furthermore, in order to seal the release hole, a second lid portion that includes a sealing portion is formed, through sputtering, on the first lid portion using a sealant of aluminum (Al) and the like.
However, when forming the sealing portion through sputtering, a part of the sealant enters the cavity via the release hole and attaches to a bottom surface of the cavity. Therefore, if a plurality of electrodes or units of wiring connected to different destinations are present on the bottom surface of the cavity immediately below the release hole, these electrodes or units of wiring could possibly be short-circuited. For this reason, traditionally, the plurality of electrodes or units of wiring connected to different destinations cannot be installed in proximity on the bottom surface of the cavity immediately below the release hole.
As related art, JP-A-2008-221435 (paragraphs 0007, 0008 and 0041, FIG. 8) discloses efficient execution of manufacturing processes of an electronic apparatus that is composed of an electronic circuit and a functional element installed in a hollow of a substrate, and that is intended to secure a manufacturing yield and reduce a manufacturing cost. This electronic apparatus has a substrate, a functional element formed on the substrate, and a covering structure that defines a hollow in which the functional element is installed. The covering structure has a layered structure made up of an inter-layer insulating film and a wiring layer that are formed on the substrate so as to surround the hollow. Out of the covering structure, at least apart of an upper covering portion, which covers the hollow from above, in a thickness direction includes a corrosion-resistant layer. The upper covering portion includes a first covering layer with a through-hole facing the hollow, and a second covering layer closing the through-hole.
On the other hand, JP-A-2010-223850 (paragraphs 0012 and 0013, FIG. 5) discloses a MEMS device that can be manufactured in simple processes, can be reduced in size, and has a highly reliable hollow space sealing structure. This MEMS device includes a substrate, a movable portion that is provided with a hole and formed on the substrate via a gap, a pillar that is formed on the substrate and penetrates into the hole without coming into contact with the movable portion, and a cap portion that is supported by the pillar and is formed on the movable portion via a gap.
JP-A-2008-221435 (paragraphs 0007, 0008 and 0041, FIG. 8) and JP-A-2010-223850 (paragraphs 0012 and 0013, FIG. 5) are examples of related art.
JP-A-2008-221435 (paragraphs 0007, 0008 and 0041, FIG. 8) states that it is preferable that the through-hole (release hole) be formed in a position shifted from a position immediately above a MEMS structural member (functional element). This makes it possible to avoid an unfavorable situation in which the material of the second covering layer attaches to the MEMS structural member at the time of formation of the second covering layer. However, JP-A-2008-221435 (paragraphs 0007, 0008 and 0041, FIG. 8) does not disclose prevention of a short circuit that occurs due to the material of the second covering layer attaching to a plurality of electrodes or units of wiring provided on a bottom surface of a cavity. JP-A-2010-223850 (paragraphs 0012 and 0013, FIG. 5) does not disclose prevention of a short circuit of a plurality of electrodes or units of wiring provided on a bottom surface of a cavity, either.